It is critical to keep an optical connector end face clean to allow for proper transmission, and thus, reduce any loss of data during use. Traditionally copper, connectors have been modified to accept termini containing optical fiber. The core of the fiber where the light is carried is roughly 9 μm for a singlemode fiber and is, typically, 50 μm or 62.5 μm for multimode fiber. Core diameters can be as large as 100 μm or greater for specialty multimode fiber. Dust particles can be of similar size—between 10 and 100 μm. Consequently, dust and grime have the potential for blocking light used to carry information. When dust is on the core of a fiber, it absorbs light that would otherwise be transmitted through the core. At best, it will attenuate some of the data being transmitted. At worst, it will absorb enough energy to burn and cause a catastrophic failure of the connector. Particles of carbon are particularly good absorbers of electromagnetic radiation and thus can heat-up very rapidly to burn. Also, during the cleaning process, the dust particles can cause damage to the connector end face as a scratch or pit that would require a repolishing to be removed.
There are many conventional methods available today for cleaning a fiber optic connector. However, each suffers from its own limitations. The most common approach depicted in the avionics maintenance manual uses specialty swabs for removing contaminants. While most experts on cleaning agree that this approach is the most effective, it unfortunately is a slow process that creates a significant amount of foreign object damage (FOD), it is costly, and the cleaning supplies are cumbersome to use in the confined spaces typically found in avionic environments.
Fiber optic connectors are typically physical contact type connectors, which means that the ceramic ferrule (with glass fiber in the middle) is physically touching the ceramic ferrule of another connector. These connectors meet end-to-end and are aligned with a ceramic alignment sleeve, or the like, to make certain that the small core of a fiber, through which the light is transmitted, is precisely aligned with the core of the mating fiber. In this way, the amount of light is transmitted across the connection interface is optimized.
When a connector is prepared, the tip of the connector, known as the end face, is ground down and polished to a smooth surface that makes it compatible with other connectors when placed face-to-face in physical contact. FIG. 1 shows the cross-section of the industry accepted geometry for a connector end face as described in GR-326. The polished surface is convex so as to ensure that the fiber's core touches before touching surrounding fiber cladding or ferrule material.
The purpose of these defined geometric requirements is to provide for physical contact of the mated fibers at all times. Fiber optic connectors work by transmitting light from one fiber across the connection interface and into the mating fiber. A certain amount of loss at this interface is unavoidable and allowed. The loss in transmission occurs from one or a combination of several different factors.
Light can be lost during transmission from the reflections at the interface, from inferior surface quality, or from an angular mismatch. Losses at the connection point can also occur due to lateral offset of the ferrules and/or fiber, angular misalignment, or an end separation which causes the two connectors not to be in physical contact.
It will be appreciated that the pressure at the end face contact point is large, and if there is any contamination at this point, damage can be done to the connector requiring a timely, labor intensive repolish.
There are several types of contamination that can occur on a connector end face, and there are several ways by which a connector can become contaminated.
Loose Contamination: Loose contamination is debris on the end face surface such as dirt, dust, streaks, oil, grease or metallic particles that are not permanent and can be removed with proper cleaning
Fixed Contamination: Fixed contamination is material on the surface that cannot be removed such as cured epoxies, stains, and embedded metallic particles.
Fixed contamination requires a repolish to remove the debris, but loose contamination can be removed, and thus avoid becoming fixed contamination (i.e. embedded material) and avoid causing a defect in the end face such as a scratch, pit, crack or chip
Contamination in the core area can block light from passing through the connector and cause high insertion loss. Also, if the contamination is a highly absorbing material such as carbon, under high power conditions it can absorb light and cause the fiber to melt. FIG. 2 shows, for example, a connector end face contaminated with oil.
Connectors can become contaminated only while they are unmated and when the end face is exposed to potential contaminants. If a connector end face comes in contact with a dirty surface while unconnected, contaminants will likely stick to the end face. This typically happens during equipment maintenance, when a technician removes a connector and fails to place a protective end cap over the ferrule. There is also the possibility of touching the connector end face with one's fingers, which is where the majority of oil contaminations originate.
Also, even in cases where a dust cap is installed while a connector is disconnected, contaminants can be introduced through the installation of the dust cap. Because of this, connectors are universally inspected before they are reinstalled into the adapter and mated to the associated connector. A universally accepted inspection template is IEC 61300-1, and in addition, many private companies have their own standards for end face acceptance.
In addition to the many more manual methods for cleaning end faces, such as KimWipes® and cotton swabs, there are many commercial-off-the-shelf (COTS) devices to clean connector end faces. The most popular device is the Cletop® (and there are several variants commercially available). This device employs a reel of cleaning material as shown in detail in FIG. 3. After depressing a lever on the device, a protective window opens and a new, clean strip of material is introduced where the technician can wipe the connector in a linear manner along the cleaning media.
This device has its limitations in that it can only clean connectors that are removed from their adapters. Most of the time both connectors cannot be removed from their adapter for cleaning. One connector will remain behind a patch panel and can only be cleaned through the adapter: There are special cleaners for this situation, an example of which is shown in FIG. 4.
This type of cleaner works much in the same way that the Cletop cleaner works in that it has a thin strip of cleaning material at its tip, which rubs along the face of the connector in order to clean it. The tip is designed to be small enough to fit into a standard adapter and further into the mating sleeve of the adapter.
Westover's Cleanblast® System utilizes a filtered stream of pressurized gas in conjuction with a vacuum to create a high flow rate jet across the surface of the fiber. A complete system requires a base unit and a cleaning tip suitable for the connector being cleaned. Portable systems have a built-in compressor and require a source of power.
Some units clean with a thin strip of cleaning media and dispense a cleaning solvent simultaneously. An internal picture of such a device is shown in FIG. 5.
It is therefore a principle object of the present invention to provide an improved apparatus and methodology for cleaning optical fiber end faces.
Yet another object of the invention is to provide optical fiber end face cleaning apparatus and methods by which cumbersome accessories need not be used.
It is yet another object of the present invention to provide improved apparatus and methodology that uses carbon nanotube technology as a cleaning media.
Other objects of the invention will be obvious and will, in part, appear hereinafter when the following detailed description is read in connection with the appended drawings.